1. Technical Field
The present disclosure relates to a driving circuit for a circuit generating an ultrasonic pulse, in particular an ultrasonic transducer.
The disclosure also relates to a corresponding driving method.
The disclosure particularly, but not exclusively, relates to an ultrasonic transducer for sonographic apparatuses able to generate ultrasonic pulses having at least one first and one second width and the following description is made with reference to this field of application for convenience of explanation only.
2. Description of the Related Art
As it is well known, sonography or ultrasonography is a diagnostic imaging technique which employs ultrasonic waves or ultrasounds and which is based on the principle of ultrasound transmission and echo reception and it is widely used in general medicine, surgery and radiology fields.
Ultrasounds being normally used are comprised between 2 and 20 MHz. The frequency is chosen by taking into account that higher frequencies have a bigger image resolution power, but penetrate less deeply into the subject under examination.
These ultrasounds are commonly generated by a piezoceramic crystal being inserted in a probe which is kept into direct contact with the skin of the subject by interposing a suitable gel (which is able to eliminate the air between the probe and the skin of the subject, thus allowing the ultrasounds to penetrate into the anatomic segment under examination). The same probe is able to receive the return or echo signal, which is suitably processed by a computer and shown onto a monitor.
In particular, ultrasounds reaching a point of change of the acoustic impedance, and thus for instance an internal organ, are partly reflected and the reflected percentage has information relating the impedance difference between the crossed tissues. It is suitable to note that, due to the big impedance difference between a bone and a tissue, sonography cannot see behind a bone, which causes a total reflection of the ultrasounds, while air or gas areas generate a “shadow”, causing a partial reflection of the ultrasounds.
Time employed by an ultrasound waves to cover the going, reflection and return path is provided to the computer, which calculates the depth wherefrom the echo is come, thus locating the division surface between the crossed tissues (corresponding to a change point of the acoustic impedance and thus to the depth wherefrom the echo comes).
Substantially, a sonographer, namely a diagnostic apparatus based on ultrasound sonography, comprises three parts:                a probe comprising at least a transducer, in particular of the ultrasonic type, which transmits and receives an ultrasound signal;        an electronic system which drives the transducer for generating the ultrasound signal or pulse to be transmitted and receives the return echo signal of such pulse from the probe, consequently processing the received echo signal; and        a displaying system of a corresponding sonographic imaging being processed starting from the echo signal as received from the probe.        
In particular, the word “transducer” generally indicates an electric or electronic device, which converts an energy type relating to mechanical and physical quantities into electric signals. In a general way, a transducer is sometimes defined as a generic device which converts energy from one form to another, in such a way that it can be further processed by men or other apparatuses. Many transducers are both sensors and actuators. An ultrasonic transducer usually comprises a piezoelectric crystal being suitably biased in order to cause its deformation and the generation of an ultrasound signal or pulse.
Ultrasound transducers for sonographic imaging are usually driven by high voltage driving circuits or drivers which are able to generate a sinusoidal signal having a variable width being comprised between 3 and 200 Vpp and frequencies between 1 MHz and 20 MHz, this sinusoidal signal being the control signal for corresponding generators of the ultrasound pulse to be transmitted, in particular piezoelectric crystals.
Frequently, the sinusoidal signal is a bipolar one, i.e., a symmetric signal with respect to a ground reference, usually equal to 0V. This however forces the drivers to be provided with a double supply reference, in other words a dual supply.
Typically, an ultrasonic transducer transmits a high voltage pulse having a length of a few μs, and receives the echo of this pulse, which is generated by its reflection on the organs of the subject under examination, for a length of around 250 μs, and then return to the transmission of a new high voltage pulse.
It is also known a transmission mode of two consecutive pulses having different width in order to modulate the transmitted power. For instance, a first pulse IM1 is alternately transmitted with a second pulse IM2 having a different width, as shown in FIG. 1 by way of example. The first pulse IM1 has a peak-to-peak sweep equal to 190 Vpp, in the shown example, while the second pulse IM2 has a smaller peak-to-peak sweep, in the example equal to 110 Vpp. Moreover, the transducer receives the corresponding echoes, as shown in FIG. 1 and indicated by E1 and E2.
In particular, these first and second pulses, IM1 and IM2, are usually generated by a pulse generator such as a piezoelectric crystal, being driven by a driver which comprises a diode halfbridge being supplied with a dual voltage having an absolute value equal to the peak voltage of the generated signal.
In order to correctly generate variable width pulses, such as the pulses IM1 and IM2 of FIG. 1, it should be however possible to instantaneously change the supply voltage value for the driver between one pulse and the subsequent one, i.e., between consecutive pulses having different widths. Practically, this known solution is thus not used in view of the high power being needed to change in few tens of μs the supply voltage value, which is in particular “burdened” by the high values of the filter capacitances, being usually connected to it.
In order to try to solve this problem, it is known to generate consecutive pulses having different width by using different circuits for generating pulses or pulse circuits being driven by different drivers. Moreover, these circuits are doubled for each transducer or channel. It is in fact known to use sonographic probes having a plurality of transducers or channels, each being able to generate a pulse and to receive a corresponding reflected pulse or echo.
In particular, multiple channel apparatuses of the known type usually comprise a plurality of aligned transducers in order to allow the generation of a linear sonographic beam.
In this case, an ultrasound probe thus comprises two pulse generator circuits, independent for each transducer or channel, each being provided with corresponding driving circuits or drivers, in particular gate driving circuits or gate drivers per diode halfbridge, independent from each other and respectively supplied with two supply pairs, HVP0, HVN0 for a first driver, or halfbridge, which controls the generation of the first pulse IM1 and HVP1, HVN1 for a second driver, or halfbridge, which controls the generation of the second pulse IM2, respectively. By taking into account the example shown in FIG. 1, it is possible to use the following values for the supply voltages of the drivers of the pulse generator circuits or halfbridges:                HVP0=+95V, HVN0=−95V,        HVP1=+55V, HVN1=−55V.        
It is immediate to understand that this known solution has a high cost due to the increase of the area and of the circuit complexity of the driving circuit or driver of the ultrasonic transducer having variable width pulses.
This increase of the area and circuit complexity turns out to be unacceptable in case of generation of 3D sonographic imaging, which uses probes comprising transducers or channel matrices, in particular up to 2500/3000 shifted channels, being able to focus the sonographic signal to provide a 3D imaging.